Most Repeated MDCAT Biology MCQs

Most-repeated Biology chapters

Each chapter below has its own page of most-repeated questions — with verified answers, explanations and the exact exam years each recurred in. Ranked by how many of its questions recur across 2+ years.

More repeated Biology questions

Repeated Biology questions from chapters that don't yet have their own page — each with the verified answer, explanation and the years it recurred.

1. 1

   Repeated in 4 yearsCell Cycle

   Cell death due to tissue damage is called:

   • ANecrosis✓
   • BMetastasis
   • CApoptosis
   • DEpistasis

   Explanation

   [A] Necrosis is the death of a body tissue,occurring when too little blood flows to the tissue.

   Appeared in the past papers of: 2010, 2011, 2013, 2023

2. 2

   Repeated in 4 yearsLipids

   Which of the following is an unsaturated fatty acid?

   • AOleic acid✓
   • BPalmitic acid
   • CButyric acid
   • DAcetic acid

   Explanation

   Unsaturated fatty acids have one or more carbon-carbon double bonds. The term unsaturated indicates that fewer than the maximum possible number of hydrogen atoms are bonded to each carbon in the molecule. Oleic acid is an example of a monounsaturated fatty acid as it has only a single double bond present in the long chain of carbons bonded to each other.Butyric acid (butanoic acid) is a 4-carbon saturated carboxylic acid. Acetic acid (ethanoic acid) is a carbon-2 saturated carboxylic acid. Palmitic acid is a 16-carbon saturated carboxylic acid.

   Appeared in the past papers of: 2012, 2020, 2023, 2024

3. 3

   Repeated in 3 yearsSome Major Ecosystems

   In Sindh, the desert ecosystem is called

   • AThar✓
   • BThal
   • CSahara
   • DGobi

   Explanation

   The desert is variously known as the Cholistan or Rohi Desert in Bahawalpur and the Pat or Thar Desert in Sindh. The surface of the desert is a wild maze of sand dunes and sand ridges.

   Appeared in the past papers of: 2015, 2016, 2017

4. 4

   Repeated in 3 yearsMiscellaneous

   Which of the following is a conjugated molecule?

   • AProtein
   • BLipid
   • CGlycoproteins✓
   • DVitamins

   Explanation

   Glycoproteins are proteins that have carbohydrate chains (glycans) attached to them. These carbohydrate chains can have various functions, such as aiding in protein folding, cell recognition, and cell signaling. Glycoproteins are examples of conjugated molecules.

   Appeared in the past papers of: 2022, 2023, 2024

5. 5

   Repeated in 3 yearsMiscellaneous

   Enzymes lower the activation energy by stabilizing the transition state of a metabolic reaction due to?

   • AChanging conditions within the active site✓
   • BChanging conditions within the protein framework
   • CRearranging the fatty acids in active site
   • DDistorting the molecules in the allosteric site

   Explanation

   Enzymes lower the activation energy by changing conditions within the active site. The active site of an enzyme is the specific region where the substrate binds and the catalytic reaction takes place. Enzymes can alter the local environment within the active site to create optimal conditions for the reaction to occur. This may involve providing specific chemical groups or ions, adjusting pH or temperature, or creating a suitable 3D arrangement of the substrate molecules. By modifying these conditions, enzymes stabilize the transition state of the reaction, making it easier for the reaction to proceed.

   Appeared in the past papers of: 2022, 2023, 2024

6. 6

   Repeated in 3 yearsMiscellaneous

   Test cross is made to check the genotype of a trait. Which of the following crosses is a test cross?

   • AUnknown x At
   • BUnknown x tt✓
   • CUnknown x AB

   Explanation

   A test cross is a cross between an individual with an unknown genotype for a particular trait and an individual that is homozygous recessive for that trait. The purpose of the test cross is to determine the genotype of the unknown individual by observing the phenotypic ratios of the offspring. This cross involves a homozygous recessive individual (tt), which is the test cross. The offspring from this cross will reveal the genotype of the unknown individual.

   Appeared in the past papers of: 2022, 2023, 2024

7. 7

   Repeated in 3 yearsMiscellaneous

   When hybrids are crossed, the genotype ratio of the offspring is

   • A1:1
   • B3:1
   • C1:2:1✓
   • D4:1
   • E3:2

   Explanation

   This is known as a monohybrid cross, involving the inheritance of a single trait (e.g., one gene with two alleles). The genotype ratio can be represented as follows: • 1/4 of the offspring are homozygous dominant (e.g., TT). • 1/2 of the offspring are heterozygous (e.g., Tt). • 1/4 of the offspring are homozygous recessive (e.g., tt). This ratio is based on Mendel's law of segregation, which describes how alleles segregate during gamete formation.

   Appeared in the past papers of: 2001, 2009, 2011

8. 8

   Repeated in 3 yearsMiscellaneous

   Which of the following diseases is sexually transmitted?

   • ATuberculosis
   • BAIDS✓
   • CDengue Fever
   • DCholera

   Explanation

   Acquired immunodeficiency syndrome (AIDS) is a chronic, potentially life-threatening condition caused by the human immunodeficiency virus (HIV). By damaging your immune system, HIV interferes with your body's ability to fight infection and disease. You can get HIV from contact with infected blood, semen, or vaginal fluids. Most people get the virus by having unprotected sex with someone who has HIV. Another common way of getting it is by sharing drug needles with someone who is infected with HIV. Hence, Option B is correct. Tuberculosis is caused by bacteria that spread from person to person through microscopic droplets released into the air.

   Appeared in the past papers of: 2018, 2020, 2024

9. 9

   Repeated in 3 yearsMiscellaneous

   Three hydrophobic fatty acid tails and a glycerol molecule join to form a _.

   • AMonoglyceride
   • BDiglyceride
   • CTriglyceride✓
   • DPhospholipids

   Explanation

   Esterification of alcohol with fatty acid results in the formation of acylglycerol, also called glyceride.When three fatty acids are involved in forming an ester bond with glycerol, a triglyceride is formed.

   Appeared in the past papers of: 2022, 2023, 2024

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